A shale damage monitoring and early warning method based on temperature and bedding angle

Abstract

The present invention belongs to the technical field of shale mechanical property detection, and specifically discloses a shale damage monitoring and early warning method based on temperature and bedding angle, comprising the following steps: obtaining the bedding angle and actual temperature of the shale, calculating the total damage variable of the coupled effect of temperature and bedding angle on rock damage based on the bedding angle and actual temperature, and using a damage model to predict the predicted compressive strength of the shale, and issuing an early warning when the predicted compressive strength exceeds the early warning threshold. The present invention systematically studies the influence of temperature and bedding angle on the mechanical properties and crack propagation patterns of shale under the synergistic effect of temperature and bedding angle, proposes a "U-shaped law" for the compressive strength of shale under different bedding angles and high temperature conditions, constructs a damage model that comprehensively considers the influence of temperature and bedding angle, quantitatively analyzes the influence of temperature and bedding angle on the compressive strength of shale, and can effectively predict the damage state of shale under different temperatures and different bedding angles.

Description

Technical Field

[0001] The present invention belongs to the technical field of shale mechanical property detection, and in particular relates to a shale damage monitoring and early warning method based on temperature and bedding angle. Background Art

[0002] As a typical layered sedimentary rock, shale has significant anisotropy, and its mechanical properties are affected by many factors. First, the bedding angle, that is, the angle between the bedding plane and the loading direction, as a basic structural characteristic of shale, directly affects its mechanical parameters such as compressive strength and elastic modulus. Secondly, changes in temperature will change the mineral composition and pore structure of shale, thereby affecting its mechanical properties. In addition, an increase in water content will weaken the strength and stiffness of shale, while changes in loading rate will affect the stress-strain response of shale. In shale mechanics research, establishing a damage model to predict compressive strength is crucial for engineering design and safety assessment.

[0003] Previous studies have analyzed the mechanical properties of shale at different bedding angles through uniaxial and triaxial compression tests. The results show that bedding angle significantly affects the compressive strength and failure mode of shale. For example, at bedding angles of 0° and 90°, shale exhibits high compressive strength, while at 45° and 60°, the compressive strength decreases significantly. Studies have also found that temperature has a significant impact on the mechanical properties of shale. As temperature increases, the compressive strength and elastic modulus of shale exhibit different trends.

[0004] Although the aforementioned studies have revealed the effects of bedding angle and temperature on the mechanical properties of shale, most of them only consider a single factor (e.g., analyzing only the effects of temperature or bedding angle on shale mechanical properties), lacking a systematic study of the coupled effects of temperature and bedding angle. Furthermore, existing damage models for predicting compressive strength have limited accuracy when considering the influence of multiple factors and are inadequate for predicting the mechanical behavior of shale under high-temperature conditions. While existing technologies have explored the tensile-shear failure mode of crack propagation, they have failed to quantitatively describe the crack propagation path and dynamic evolution mechanism at different bedding angles. Most existing mechanical property prediction models only consider the influence of a single factor and have failed to construct a damage prediction model that comprehensively considers multiple factors such as temperature and bedding angle. Summary of the Invention

[0005] In response to the above-mentioned problems, the purpose of the present invention is to provide a shale damage monitoring and early warning method based on temperature and bedding angle, and to construct a damage model that comprehensively considers the influence of temperature and bedding angle, which can effectively predict the damage status of shale under different temperature and different bedding angle conditions.

[0006] The technical solution of the present invention is: a shale damage monitoring and early warning method based on temperature and bedding angle, comprising the following steps:

[0007] The bedding angle and actual temperature of the shale are obtained, and the total damage variable of the coupled effect of temperature and bedding angle on shale damage is calculated based on the bedding angle and actual temperature.

[0008] According to the total damage variable of the coupled effects of temperature and bedding angle on shale damage, the predicted compressive strength of shale is predicted using the damage model shown below.

[0009] ,in, represents the predicted compressive strength of shale, Indicates the compressive strength under reference conditions, The total damage variable represents the coupled effects of temperature and bedding angle on shale damage.

[0010] An early warning is issued when the predicted compressive strength exceeds the early warning threshold.

[0011] Furthermore, the calculation of the total damage variable of the coupled effect of temperature and bedding angle on shale damage based on the bedding angle and the actual temperature includes:

[0012] Determine bedding angle damage variables based on bedding angle .

[0013] Determine the temperature damage variable based on the actual temperature .

[0014] The variables are weighted and summed, and the total damage variable of the coupled effect of temperature and bedding angle on shale damage is obtained according to the following formula.

[0015] ,in, , and Both represent weighting coefficients, represents the contribution of temperature to the overall damage, represents the contribution of bedding angle to the overall damage, Indicates the actual temperature, Indicates the bedding angle.

[0016] Furthermore, the bedding angle is determined according to the following formula to determine the bedding angle damage variable: The stress-strain relationship of a material can be expressed as: The stress-strain relationship of a material can be expressed as: The stress-strain relationship of a material can be expressed as: The stress-strain relationship of a material can be expressed as: The stress-strain relationship of a material can be expressed as: The stress-strain relationship of a material can be expressed as:

[0017] ;in, represents the bedding angle, represents the minimum bedding damage value, Indicates the maximum bedding damage value.

[0018] Furthermore, the actual temperature determines the damage variable according to the following formula: .

[0019] ;in, represents the temperature damage coefficient, Indicates the actual temperature, Indicates the reference temperature.

[0020] Furthermore, the specific steps of determining the weighted coefficient of the weighted summation are:

[0021] Multiple shale samples were obtained by drilling at different bedding angles. Axial loads were applied to these samples at different temperatures, and the acoustic characteristics of the shale damage and fracture processes were detected. The weighted coefficients for the weighted summation were calculated.

[0022] Furthermore, the bedding angles are 0° to 90°.

[0023] Furthermore, the specific steps for applying axial loads to multiple shale samples are as follows: encapsulating the shale samples in plastic tubes and attaching an acoustic emission monitoring device to the surface of the shale samples. The shale samples are then heated to different temperature stages. After reaching each target temperature stage, the temperature is maintained constant for one day, and an axial compressive load is applied using a displacement-controlled mode. During the loading process, the acoustic emission monitoring device monitors the initiation and growth of cracks within the samples in real time, and records the characteristic parameters of the acoustic emission signals.

[0024] Furthermore, the shale sample is heated at a heating rate of 3° C. / min.

[0025] Furthermore, the loading rate of the axial compression load is set to 0.1 mm / min.

[0026] Furthermore, the acoustic emission signal is analyzed according to the formula k=AF / RA. When k is greater than 50, it is determined to be tensile failure, and when k is less than 50, it is determined to be shear failure. RA represents the ratio of the rise time to the maximum amplitude of the acoustic emission signal, which is used to characterize the failure type. AF represents the ratio of the ring count to the duration of the acoustic emission signal, which is used to evaluate the signal characteristics.

[0027] Compared with the existing technology, the beneficial effects of the present invention are: the present invention systematically studies the influence of temperature and bedding angle on the mechanical properties and crack propagation mode of shale, proposes a "U-shaped law" of shale compressive strength under different bedding angles and high temperature conditions, constructs a damage model that comprehensively considers the influence of temperature and bedding angle, quantitatively analyzes the influence of temperature and bedding angle on the compressive strength of shale, and can effectively predict the damage state of shale under different temperatures and different bedding angles. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 1 is a relationship diagram between uniaxial compressive strength and bedding angle of different experimental groups of the experimental examples of the present invention.

[0029] Figure 2 3 is a graph showing the change in elastic modulus at different bedding angles in the experimental example of the present invention.

[0030] Figure 3 This is the stress-strain curve under different bedding angles and temperature conditions of the experimental example of the present invention.

[0031] Figures 4 to 6 is a comparison diagram of acoustic emission parameters under different bedding angles in the experimental example of the present invention; wherein, Figure 4 This is a comparison chart of ringing count parameters at different bedding angles; Figure 5 It is a comparison chart of amplitude parameters under different bedding angles; Figure 6 This is a comparison chart of energy parameters at different bedding angles.

[0032] Figure 7 These are the acoustic emission characteristics of tensile cracks and shear lines at different bedding angles in the experimental examples of the present invention.

[0033] Figure 8 These are the acoustic emission modes of tensile failure and shear failure at different bedding angles and temperatures in the experimental examples of the present invention.

[0034] Figure 9 This is a comparison chart of the number of acoustic emission events at different bedding angles and temperatures in the experimental example of the present invention. DETAILED DESCRIPTION

[0035] The following combination Figures 1 to 9 , a detailed description of the specific embodiments of the present invention is provided. In the description of the present invention, it should be understood that the terms "center," "upper," "lower," "front," "back," "left," "right," "vertical," "horizontal," "top," "bottom," "inside," "outside," and the like, indicating positions or location relationships, are based on the positions or location relationships shown in the accompanying drawings and are intended only to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed or operate in a specific orientation, and therefore should not be construed as limiting the present invention.

[0036] The terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, features specified as "first" or "second" may explicitly or implicitly include one or more of such features; in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0037] Example

[0038] A shale damage monitoring and early warning method based on temperature and bedding angle includes the following steps:

[0039] The bedding angle and actual temperature of the shale are obtained, and the total damage variable of the coupled effect of temperature and bedding angle on shale damage is calculated based on the bedding angle and actual temperature.

[0040] According to the total damage variable of the coupled effects of temperature and bedding angle on shale damage, the predicted compressive strength of shale is predicted using the damage model shown below.

[0041] ,in, represents the predicted compressive strength of shale, Indicates the compressive strength under reference conditions, The total damage variable represents the coupled effects of temperature and bedding angle on shale damage.

[0042] An early warning is issued when the predicted compressive strength exceeds the early warning threshold.

[0043] Preferably, the total damage variable of the coupled effect of temperature and bedding angle on shale damage is calculated based on the bedding angle and the actual temperature, including:

[0044] Determine bedding angle damage variables based on bedding angle .

[0045] Determine the temperature damage variable based on the actual temperature .

[0046] The variables are weighted and summed, and the total damage variable of the coupled effect of temperature and bedding angle on shale damage is obtained according to the following formula.

[0047] ,in, , and Both represent weighting coefficients, represents the contribution of temperature to the overall damage, represents the contribution of bedding angle to the overall damage, Indicates the actual temperature, Indicates the bedding angle.

[0048] Preferably, the bedding angle is determined according to the following formula to determine the bedding angle damage variable: .

[0049] ;in, represents the bedding angle, represents the minimum bedding damage value, Indicates the maximum bedding damage value.

[0050] Preferably, the actual temperature determines the damage variable according to the following formula .

[0051] ;in, represents the temperature damage coefficient, Indicates the actual temperature, Indicates the reference temperature.

[0052] Preferably, the specific steps of determining the weighted coefficient of the weighted summation are:

[0053] Multiple shale samples were obtained by drilling at different bedding angles. Axial loads were applied to these samples at different temperatures, and the acoustic characteristics of the shale damage and fracture processes were detected. The weighted coefficients for the weighted summation were calculated.

[0054] Preferably, the bedding angles are 0° to 90°. The bedding angles are selected in the full range of 0° to 90°, which can effectively ensure that the model obtained later is the optimal model. This is mainly because the shale samples at each bedding angle are collected comprehensively to obtain the optimal model. and The value of .

[0055] Preferably, the specific steps for applying an axial load to the multiple shale samples are as follows: encapsulating the shale samples in a plastic tube and securing an acoustic emission monitoring device to the surface of the shale samples. The shale samples are heated to different temperature stages, maintained at a constant temperature for one day after reaching each target temperature stage, and an axial compressive load is applied using a displacement-controlled mode. During the loading process, the acoustic emission monitoring device is used to monitor the initiation and propagation of cracks within the samples in real time, and characteristic parameters of the acoustic emission signals are recorded.

[0056] Preferably, the shale sample is heated at a heating rate of 3°C / min.

[0057] Preferably, the loading rate of the axial compression load is set to 0.1 mm / min.

[0058] Preferably, the acoustic emission signal is analyzed according to the formula k=AF / RA, and when k is greater than 50, it is determined to be tensile failure, and when k is less than 50, it is determined to be shear failure; RA represents the ratio of the rise time to the maximum amplitude of the acoustic emission signal, which is used to characterize the failure type, and AF represents the ratio of the ring count to the duration of the acoustic emission signal, which is used to evaluate the signal characteristics.

[0059] Experimental example

[0060] An experiment was conducted based on the shale damage monitoring and early warning method proposed in the embodiment, and the specific steps are as follows:

[0061] S1. Prepare shale samples.

[0062] The shale samples were collected from the Gulong shale oil block within the Q3 section of the Qingshankou Formation. This block features organic-rich, gray-black to dark gray carbonaceous shale formations with a distinct layered structure, complex interlayering, and weak cohesion, making them susceptible to weathering. The formation has an overall dip angle of 60°, indicating a complex tectonic history.

[0063] In order to ensure the representativeness and consistency of the samples, shale samples with relatively stable and less disturbance in the deep formation were selected in the experiment. In order to study the influence of bedding angle on the mechanical properties and failure mode of shale, samples were drilled at bedding angles of 0°, 30°, 45°, 60° and 90°, respectively. Figure 1 As shown in Figure 2, samples were processed into cylinders with a diameter of 25 mm and a length of 50 mm according to the International Society of Shale Mechanics (ISRM) standards to ensure standardization and repeatability of the test. By selecting different bedding angles, the effect of bedding on the damage and failure modes of shale under uniaxial compression at in situ temperature was systematically investigated.

[0064] S2. An axial load test is performed on the shale sample, and the acoustic characteristics of the shale during damage and fracture are detected. The characteristic parameters of the acoustic emission signal are recorded to obtain experimental data.

[0065] A mechanical testing device was used to apply an axial load to the shale sample, and an acoustic emission monitoring device was used to detect the acoustic characteristics of the shale damage and fracture process. The GCTS RTR-1500 shale mechanical testing system was used, which has precise temperature and pressure control functions and can accurately apply axial loads. The temperature control system required in this system includes a high-temperature heating device and a high-precision temperature sensor for real-time monitoring and adjustment of the temperature during the experiment. The temperature range of the high-temperature heating device is from room temperature to 160°C, and the accuracy of the high-precision temperature sensor is ±1°C. The sample is encapsulated in a plastic tube to maintain temperature stability and avoid external interference. The real-time monitoring system ensures precise temperature control during the heating process, avoiding temperature fluctuations during traditional preheating and constant temperature processes.

[0066] The acoustic emission monitoring system used in this system uses the DS-5 system from Beijing Ruandao Company, which monitors the initiation and propagation of cracks within the shale in real time. The acoustic emission signal's resonant frequency is 140 kHz, the preamplifier gain is set to 40 dB, and the signal acquisition threshold is 35 dB. Signal characteristics such as ring counts, cumulative events, and energy are analyzed to reveal the acoustic behavior of shale damage and fracture processes at in situ temperatures.

[0067] The shale sample was firmly mounted in the GCTS RTR-1500 system, and six acoustic emission sensors were fixed to the sample surface by a clamp, and the wiring was ensured to be correctly connected to the data acquisition system. The sample was heated using a real-time high temperature system, and the heating rate was set to 3°C / minute. It was heated to three temperature stages of 100°C, 130°C and 160°C respectively. After reaching the target temperature, the temperature was kept constant for one day to ensure that the sample was fully heated. Under constant temperature conditions, the axial compression load was applied using the displacement control mode, and the loading rate was set to 0.1mm / min to ensure accurate capture of the stress-strain curve. During the loading process, the acoustic emission system monitored the initiation and expansion of cracks inside the sample in real time, and recorded the relevant acoustic emission signal characteristic parameters.

[0068] S3. Analyze the experimental data and draw experimental conclusions.

[0069] like Figure 1 、 Figure 2 As shown in the figure, the uniaxial compressive strength of shale shows a "first decrease, then increase" trend with bedding angle. At bedding angles of 0° and 90°, the compressive strength reaches its maximum value, while significantly decreasing at bedding angles of 45° and 60°. This reflects the influence of the interaction between bedding direction and loading direction on the internal microstructure and mechanical properties of shale. In addition, the elastic modulus of shale decreases significantly with increasing bedding angle. At a bedding angle of 0°, the elastic modulus is the highest. As the bedding angle increases, especially at angles of 45° and 60°, the stiffness decreases significantly, exhibiting stronger plastic deformation characteristics.

[0070] like Figure 3 As shown in the figure, at bedding angles of 0° and 90°, the peak stress of shale is relatively high, especially exceeding 300 MPa at 100°C and 130°C. In contrast, at bedding angles of 45° and 60°, the peak stress decreases significantly with increasing temperature, especially at the combination of 160°C and 45°, where the strength decreases significantly and the plastic zone expands.

[0071] like Figures 4 to 6As shown in the figure, the variation pattern of acoustic emission parameters under different bedding angles shows that, among them, the acoustic emission parameters are ring count, amplitude and energy. At low bedding angles, acoustic emission events are frequent and energy release is strong, and cracks extend smoothly along the bedding plane. For example, the low bedding angle is 0°. As the bedding angle increases, the number of acoustic emission events decreases and the energy release decreases. Especially at 90°, the acoustic emission signal becomes sparse and crack extension is hindered. Figure 4 This is a comparison chart of ringing count parameters at different bedding angles; Figure 5 It is a comparison chart of amplitude parameters under different bedding angles; Figure 6 This is a comparison chart of energy parameters at different bedding angles.

[0072] like Figure 7 As shown in the figure, the ratio of acoustic emission parameters clearly distinguishes between tensile and shear failure. RA represents the ratio of the acoustic emission signal's rise time to its maximum amplitude, used to characterize the failure type, while AF represents the ratio of the acoustic emission signal's ring count to its duration, used to assess signal characteristics. When the AF / RA ratio exceeds the critical value k=50, it is considered tensile failure; below 50, it is shear failure. The failure mode transitions from tensile to shear at different bedding angles, with shear failure increasing significantly at bedding angles of 30°, 45°, and 60°.

[0073] like Figure 8 As shown in the figure, at bedding angles of 0° and 90°, tensile failure dominates, while at angles of 30°, 45°, and 60°, shear failure increases significantly. Under high temperature conditions, the shear failure ratio is highest, especially at a bedding angle of 60°, further verifying the synergistic effect of bedding angle and temperature on the failure mode.

[0074] like Figure 9 As shown in the figure, the number of acoustic emission events at different bedding angles is highest at a bedding angle of 60° and lowest at an angle of 90°. As the temperature increases, the number of acoustic emission events peaks at intermediate bedding angles, ranging from 45° to 60°, indicating that the combination of high temperature and intermediate bedding angles is more likely to induce complex failure modes.

[0075] S4. Establish a damage model based on experimental conclusions.

[0076] To accurately predict the effects of temperature and bedding angle on the compressive strength of shale, a damage model that considers the effects of temperature and bedding angle was developed based on shale damage mechanics theory. This model, fitted with experimental data, can predict the compressive strength of shale at different temperatures and bedding angles (specifically, 100°C, 130°C, and 160°C) and at different bedding angles (0°, 30°, 45°, 60°, and 90°).

[0077] According to the theory of continuum damage mechanics, the material will produce internal damage under external load, resulting in a reduction in the effective bearing area.

[0078] The traditional damage variable D1 is defined as: Where D1 represents the traditional damage variable, A represents the effective bearing area after damage, and A0 represents the initial bearing area.

[0079] The stress-strain relationship of the material can be expressed as: . Where σ represents stress, E represents elastic modulus, Indicates strain.

[0080] Temperature affects shale damage by causing microcrack expansion and mineral phase change through thermal stress. The temperature damage variable is calculated according to the following formula.

[0081] ;in, represents the temperature damage variable, represents the temperature damage coefficient, Indicates the actual temperature, Indicates the reference temperature.

[0082] The bedding angle affects the anisotropic mechanical behavior of shale, and the bedding angle damage variable is calculated according to the following formula.

[0083] ;in, represents the bedding angle damage variable, represents the bedding angle, represents the minimum bedding damage value, Indicates the maximum bedding damage value.

[0084] A newly designed bedding angle damage variable formula is used to describe the bedding angle The influence of shale damage. The formula is combined with the minimum bedding damage value by the sine and cosine functions of the bedding angle and maximum bedding damage value , introduces a continuous influence model for bedding angle, reflecting the nonlinear effect of angle variations on damage. This formula accurately quantifies the impact of bedding angle on shale damage, overcoming the shortcomings of existing technologies that lack systematic and precise quantification of the impact of bedding angle. Most existing technologies treat the impact of bedding angle in a simplistic or inaccurate manner, failing to account for the continuous and nonlinear effects of complex variations in bedding angle on shale damage.

[0085] The total damage variable of the coupled effects of temperature and bedding angle on shale damage is calculated according to the following formula.

[0086] ,in, , The total damage variable represents the coupled effects of temperature and bedding angle on shale damage, and Both represent weighting coefficients, represents the contribution of temperature to the overall damage, represents the contribution of bedding angle to the overall damage, represents the temperature damage variable, represents the bedding angle damage variable.

[0087] The predicted compressive strength of shale is predicted using the damage model shown below.

[0088] ,in, represents the predicted compressive strength of shale, i.e., the compressive strength of shale under temperature damage variables and bedding angle damage variables, Indicates the compressive strength under reference conditions.

[0089] By adjusting the temperature damage variable and bedding angle damage variables The coupling relationship is innovatively expressed, and two weighted coefficients are defined and , representing the contributions of temperature and bedding angle to overall damage, respectively. The effects of temperature and bedding angle are quantified into an overall damage model through two weighting coefficients. This weighted synthesis model can flexibly combine the different effects of temperature and bedding angle and determine their relative contributions based on experimental data. This innovation fills the gap in the existing technology of the lack of multi-factor coupling models, can more accurately predict the mechanical properties of shale under complex conditions, and provides a more scientific and accurate prediction tool for mechanical behavior under the combined influence of high temperature and bedding angle.

[0090] In order to accurately predict the compressive strength of shale at different temperatures and bedding angles, uniaxial compression tests were conducted on shale samples at different temperatures, and the influence of bedding angles was analyzed experimentally. The following key parameters were obtained: base temperature Compressive strength at 0℃, reference conditions is 120MPa, the temperature damage coefficient 0.004℃ -1 , minimum bedding damage value is 0.05, the maximum bedding damage value is 0.55, which is calculated , then the total damage variable of the coupled effect of temperature and bedding angle on shale damage is .

[0091] S5. Predict the predicted compressive strength of shale at different temperatures and different bedding angles based on the damage model, and issue an early warning when the predicted compressive strength exceeds an early warning threshold.

[0092] For the first time, the synergistic effect of temperature and bedding angle was systematically studied, and a "U-shaped law" was proposed to describe the changes in compressive strength under different bedding angles. A damage model for predicting compressive strength that comprehensively considers the effects of temperature and bedding angle was established. Through this innovative approach, the limitations of existing research that ignore the interaction of multiple factors were overcome. According to the experimental results, the compressive strength of shale shows a "U-shaped" distribution with changes in bedding angle. Specifically: When the bedding angle is 0° and 90°, the compressive strength of shale reaches its maximum value. At bedding angles of 45° and 60°, the compressive strength decreases significantly.

[0093] This indicates that the bedding angle has a significant effect on the compressive strength of shale, and at certain angles, such as 45° and 60°, the compressive strength decreases due to the effect of temperature.

[0094] The "U-shaped law" is reflected through experimental data and mechanical properties analysis. It is specifically reflected in the following content: Experimental results analysis: Figure 1 A graph showing the relationship between uniaxial compressive strength and bedding angle for different experimental groups shows the effect of bedding angle on compressive strength, which exhibits a "U-shaped pattern." The experimental data indicates that shale has high compressive strength at bedding angles of 0° and 90°, while the compressive strength decreases significantly at bedding angles of 45° and 60°.

[0095] An experimental plan covering different temperatures and bedding angles was designed, which comprehensively covered the temperature and bedding angle changes that may be encountered under actual geological conditions, thereby obtaining more accurate experimental data.

[0096] By optimizing the positioning accuracy of acoustic emission signals and the method of identifying failure modes, a quantitative crack propagation monitoring method combining the characteristics of acoustic emission signals was proposed, providing more efficient and reliable technical support for real-time monitoring and failure early warning.

[0097] A damage model for predicting compressive strength that comprehensively considers the effects of temperature and bedding angle was constructed. The accuracy of this damage model was verified using experimental data. Compared to existing technologies, this model is capable of providing accurate predictions under complex conditions. Through detailed sample preparation, precise experimental equipment and procedures, comprehensive analysis of experimental results, and mathematical modeling based on damage mechanics theory, the compressive strength of shale can be effectively predicted under different temperatures and bedding angles. The damage model validation results demonstrate the high accuracy of the early warning method, providing reliable theoretical support and scientific basis for evaluating the mechanical behavior of shale in shale oil production.

[0098] It should be noted that step S3 analyzes experimental data, including experimental measurements of shale mechanical properties at different temperatures and bedding angles, such as compressive strength, elastic modulus, and stress-strain curves. This analysis of experimental data allows the fitting of model parameters, such as the temperature damage coefficient and bedding damage parameter, and provides the foundation for constructing the damage model in the subsequent step S4. The damage model in step S4 is fitted based on the experimental results from step S3, and the accuracy of the predictions is verified based on these experimental results.

[0099] For the first time, this study systematically investigated the synergistic effects of temperature and bedding angle, proposing a "U-shaped law" to describe the variation in compressive strength at different bedding angles. Furthermore, a damage model for predicting compressive strength was established that comprehensively considers the effects of both temperature and bedding angle. This innovative approach overcomes the limitations of existing research that often neglects the interaction of multiple factors.

[0100] The experimental scheme covers different temperatures and different bedding angles, which comprehensively covers the temperature and bedding angle changes that may be encountered under actual geological conditions, thereby obtaining more accurate experimental data.

[0101] By optimizing the positioning accuracy of acoustic emission signals and the method of identifying failure modes, a quantitative crack propagation monitoring method combining the characteristics of acoustic emission signals was proposed, providing more efficient and reliable technical support for real-time monitoring and failure early warning.

[0102] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and do not limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of protection of the present invention.

Claims

1. A shale damage monitoring and early warning method based on temperature and bedding angle, characterized in that: The following steps are involved: Obtain the bedding angle and actual temperature of the shale, and calculate the total damage variable of the coupled effect of temperature and bedding angle on shale damage based on the bedding angle and actual temperature; Based on the total damage variable of the coupled effects of temperature and bedding angle on shale damage, the predicted compressive strength of shale is predicted using the damage model shown below; ； in, represents the predicted compressive strength of shale, Indicates the compressive strength under reference conditions, The total damage variable represents the coupled effects of temperature and bedding angle on shale damage; Issue an early warning when the predicted compressive strength exceeds the early warning threshold; The total damage variable of the coupled effect of temperature and bedding angle on shale damage is calculated based on the bedding angle and the actual temperature, including: Determine bedding angle damage variables based on bedding angle ; Determine the temperature damage variable based on the actual temperature ; The variables are weighted and summed to obtain the total damage variable of the coupled effects of temperature and bedding angle on shale damage according to the following formula: ,in, , and Both represent weighting coefficients, represents the contribution of temperature to the overall damage, represents the contribution of bedding angle to the overall damage, Indicates the actual temperature, Indicates bedding angle; The bedding angle is determined by the following formula to determine the bedding angle damage variable ; ;in, represents the bedding angle, represents the minimum bedding damage value, represents the maximum bedding damage value; The actual temperature determines the damage variable according to the following formula ; ;in, represents the temperature damage coefficient, Indicates the actual temperature, Indicates the reference temperature; The specific steps of determining the weighted coefficient of the weighted summation are: Samples were drilled at different bedding angles to obtain multiple shale samples; Axial loads were applied to multiple shale samples at different temperatures, and the acoustic characteristics of the shale damage and fracture process were detected. The weighted coefficients of the weighted summation were calculated. The bedding angle range is 0°~90°.

2. The shale damage monitoring and early warning method based on temperature and bedding angle according to claim 1, characterized in that: The specific steps of applying axial load to the plurality of shale samples are as follows: The shale sample is encapsulated in a plastic tube, and the acoustic emission monitoring device is fixed on the surface of the shale sample; The shale samples were heated to different temperature stages. After reaching the target temperature stage, the temperature was kept constant for one day, and an axial compressive load was applied using a displacement control mode. During the loading process, the acoustic emission monitoring device is used to monitor the initiation and propagation of cracks inside the sample in real time, and the characteristic parameters of the acoustic emission signal are recorded.

3. The shale damage monitoring and early warning method based on temperature and bedding angle according to claim 2, characterized in that: The shale sample was heated at a heating rate of 3°C / min.

4. The shale damage monitoring and early warning method based on temperature and bedding angle according to claim 2, characterized in that: The loading rate of the axial compression load was set to 0.1 mm / min.

5. The shale damage monitoring and early warning method based on temperature and bedding angle according to claim 2, characterized in that: The acoustic emission signal is analyzed according to the formula k=AF / RA. When k is greater than 50, it is determined to be tensile failure, and when k is less than 50, it is determined to be shear failure. RA represents the ratio of the rise time to the maximum amplitude of the acoustic emission signal, which is used to characterize the failure type. AF represents the ratio of the ring count to the duration of the acoustic emission signal, which is used to evaluate the signal characteristics.

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